1. Field of the Invention.
This invention relates to an electronic method for determining whether or not aluminum particles are suitable for use as a rocket propellant fuel.
2. Description of the Prior Art.
The use of aluminum particles as a fuel in solid rocket propellants is, of course, well known. It is also well known that aluminum powder is not really aluminum but rather aluminum coated with aluminum oxide.
Aluminum powder, i.e., aluminum particles coated with aluminum oxide, comes to those who manufacture solid rocket propellants from several different sources. Perhaps because each source has at least some unique techniques which it uses in the manufacture of aluminum powder, i.e., techniques which are different than those used by any other company, aluminum powder varies from source to source. More specifically, properties of the aluminum oxide coatings on aluminum particles vary depending on the source. Aluminum particles and, more specifically, the oxide coatings thereon even may vary from batch to batch when they are obtained from a single source.
High speed photography has recently shown that the oxide coatings on aluminum particles have much to do with how effective aluminum particles are insofar as their fuel qualities in a solid propellant are concerned. When as-purchased aluminum particles are used, they tend to agglomerate when heated. Agglomeration is undesirable. Accordingly, a method was developed for treating aluminum particles to render the coatings of oxide thereon more uniform and to heal the coatings, i.e., heal any flaws or scratches in the coatings where pure aluminum might be "peeking" through. The method involves strengthening the aluminum oxide coatings by baking the particles for from 10 to 35 hours at 560.degree.C under 1 atmosphere of oxygen. High speed photography of burning rocket propellant grains has indicated that this process is very effective in reducing agglomeration.
In order to determine how long one should bake aluminum particles in the above-described process, for example, 10, 11, 12, . . . , 35 hours, it is necessary to test the particles. This could be done, of course, by baking small batches for 10, 11, 12, . . . , 35 hours, incorporating the batches into separate solid rocket propellant grains, burning the grains and observing the results with high speed photographic equipment. This would, however, obviously be a long, drawn out testing process. It is, accordingly, the primary objective of this invention to provide a simple, fast and effective method for testing powdered aluminum to determine whether or not it is suitable for use as a rocket propellant fuel.